1. Field of the Invention
The present invention relates to a buffering air-bag means and, more particularly, a buffering air-bag means which comprises a gas generating means mounted at a front face portion of the hub of a steering wheel and an air-bag which is normally folded around said gas generating means and is adapted to be inflated by the gas generated by said gas generating means to occupy a space in front of said steering wheel so as to provide a buffering body for the driver when a collision which produces a shock exceeding a predetermined level has occurred.
2. Description of the Prior Art
Since the air-bag means of the abovementioned type is mounted at the front face portion of a steering wheel hub, it must be constructed as small and compact as possible so that its mass or inertia does not affect the driving performance of the automobile and it does not disturb the driver in operating the steering wheel or observing various gauges mounted in the dash board. The volume of the air-bag means in its unactuated condition wherein the air-bag is folded, is determined principally by the volume of the gas generating means. The volume of the gas generating means or the volume of a box which forms an outer shell thereof is determined not only by the volume required for loading gas generating chemical substances, additives and a filter for cinders generated by the reaction of the chemical substances but also by the condition regarding the gas ejecting openings. When a collision has occurred, gas is ejected from the gas generating means at a high ejecting speed to rapidly inflate the air-bag. If the gas jet has a velocity component in the direction of the axis of the steering column, the column is exerted with a compression force in its axial direction. This compression force reduces the shock absorbing capacity of a steering column of a shock energy absorbing type, thereby damaging the buffering performance of the steering column. Therefore, in the conventional gas generating means, the box which forms the outer shell of the gas generating means is generally formed as a cylindrical body having closed opposite ends, while its cylindrical side wall is formed with gas ejecting openings so that the gas is ejected only in radial directions which are substantially perpendicular to the axis of the steering column.
Furthermore, in the conventional gas generating means, there is another problem in that the gas ejecting velocity can not be increased beyond a limit in view of cinder ejection, because if the gas ejecting velocity is very high, hot cinder particles ejected together with the gas impinge upon the wall of the air-bag thereby causing damage to the air-bag. Therefore, if a determined inflation performance of the air-bag is to be obtained under a limited gas ejecting velocity, the opening area of the gas ejecting openings must be increased, thereby causing a relatively large volume of the gas generating means.
An example of the conventional buffering air-bag means and the outer shell box of its gas generating means are shown in FIGS. 1 and 2, respectively. As shown in these figures, a gas generating means 1 is formed as a cylindrical body composed of a disc-like end wall 2, a cylindrical side wall 3 and an end wall 4 which closes the opposite end of the cylindrical body while providing a flange of mounting the gas generating means. The cylindrical side wall 3 alone is formed with a number of gas ejecting openings 5. In this box structure of the gas generating means, since the end wall 2 is not formed with gas ejecting openings, the cylindrical side wall 3 must have a relatively large height in order that the gas ejecting openings of a sufficient opening area are provided in the cylindrical side wall 3. When the gas generating means is mounted at a hub portion 7 of the steering wheel 6 together with an air-bag 8 mounted therearound and folded as shown in FIG. 1, the folded portion of the air-bag is generally arranged at side portions of the cylindrical gas generating means to avoid a further increase in the height of the air-bag means. In FIG. 1, element 9 designates a pad which encloses the folded air-bag.
As apparent from FIG. 1, the conventional air-bag means has the drawback that the height and diameter of the air-bag means in its stored condition covered by the pad 9 are relatively large and, therefore, the height h of a steering wheel of a cone type must be increased, resulting in a large steering wheel. The big air-bag means prevents the driver from having a good view of various gauges mounted into the dashboard, thus affecting the drivability of the automobile.
The outer shell box is conveniently made by joining two cup members each being produced by the art of deep pressing. In this case, the gas ejecting openings can not be formed in a plate material before the application of deep pressing, because the plate material is much deformed by the deep pressing, thus making it almost impossible to obtain a final opening of a required shape and dimension from a preformed opening. Therefore said cup member is first produced from a blank plate and, thereafter, the gas ejecting openings are formed by drilling in the cylindrical side wall of the cup member. However, it requires substantial work and cost to form a number of radial openings in a cylindrical wall by drilling. Furthermore, it is difficult and inefficient to fold the air-bag 8 around the cylindrical gas generating means which further increases the manufacturing cost.